Tracer and tool for engraving-machines.



PATENTED APR. 3, 1906.

M. BARR.

TRACER AND TOOL FOR BNGRAVING MACHINES.

APPLICATION FILED FEB. 6. 1993.

i f 1 IT STATES PATENT OFFICE.

MARK BARR, OF LONDON, ENGLAND, ASSIGNOR, BY MESNE ASSIGNMENTS, TO LINOTYPE 8: MACHINERY LIMITED, OF LONDON, ENGLAND.

TRACER AND TOOL FOR ENGRAVING-IVIACHINES.

Specification of Letters Patent. I

Patented April 3, 1906.

Original application filed October 13 1900, Serial No. 32,999. Dividedand this application filedPebruary 6, 1903. Serial No. 142,686.

To all whom, it nuty cmwern:

new and useful Improvements in the Tracers and Tools ofEngraving-Machines; and I do hereby declare the following to be a full,clear,

and exact description of the invention, such as will enable othersskilled in the art to which it appertains to make and use the same.

The present invention consists in improved tracers and tools for use inan engraving-machine.

It is a division from my pending application Serial No. 32,999, filedOctober 13, 1900.

In any engravingmachine such, for instance, as the well-knownBenton-Waldo or the Ballou engraving-machines-for producing objectswhich, like dies, have three dimensionslength, width, and depth ofdesign it is essential that the cutting edges of the tool shall have thesame form as the tracer end, the dimensions of those edges being at thesame time modified according to the desired ratio between pattern andobject. In all such engraving-machines it is the motion of the axis ofthe tracer end which is transmitted to and reproduced proportionally andwith more or less accuracy in the axis of the tool; but as the tracerend has necessarily a finite thickness the pattern will be touched asthe said end is moved over it by points in the surface of the tracer endwhich are radially on one side of the axis of that end. Consequently itis the motions of those points as distinguished from the motions ofpoints situated in the said axis and in the same horizontal plane thatare reproduced in homologous points in the surface of the tool.

Now I am convinced that the principles laid down in the precedingparagraph have not been appreciated hitherto at their true value or havenot been carried into effect.

An engraving-machine is called upon to produce objects in many ratios.That has hitherto necessitated an indefinitely large number of tools,soas to be ready for an object in any ratio to the pattern. Further, as itis impracticable to grind a tool held in any head-stock other than theone in which it is to be used a corresponding number of headstocks, eachholding the respective tool, is a second necessity, and, furthermore,when a tool is wanted to work to a given ratio it must be ground to thenecessary form at a moments notice.

Referring to the accompanying drawings,

which are to be taken as part of this specification and read therewith,Figures 1 and 2 are side elevations of two different forms of tracerends, showing the efiect of varying re lations of the elements D and Rand Figs. 3

and 4 are side elevations, drawn to an exaggerated scale, of portions ofa tracer and tool, respectively, the operating ends of which haverelationships according to the present invention.

One result of the present invention is that the tracerrrod is equippedwith only a comaratively small number of tracer ends. The forms of theseends are such as will be convenient generallysay, blunt, curved,ballpointed, and sharp. These ends are for tracing over any patternwhich may be brought to the engraving-machine to be worked from, and foreach ratio between pattern and object corresponding tools are ground.

The present invention requires that the form (using this word asincluding all the geometric elements) of each of the tracer endsmentioned in the preceding paragraph shall be one that is easilyexpressed by one or more simple elements or coordinates. These appearfirst in the tracer end to be afterward reproduced in the tool. Theeasiest process for giving the desired form to a tracer end is wellknown to users of engraving-machines to be one of grinding, the ungroundend being held up to the grinder at right angles with its surface androcked about a center of oscillation situated somewhere along the axisof the tracer end or to one side thereof. Now the radius R of thecurvature of the ground end and the distance D of the center ofoscillation from the axis of the tracer end, (see Fig. 1,) are the twosimple elements or c0- ordinates above mentioned, and their respectivedimensions settle the form of the tracer end. If R be infinite and D bezero, there will not be any curvature at all, although such a case wouldnot occur in the practical use of the invention. If, as indicated inFig. 2, R equals the radius of the cross-section of the unformed tracerend and D be zero, the form of that end will be hemispherical, and itwill acquire acuteness in proportion as D is made longer, as Will be ifH readily appreciated from a comparison of Figs. 1 and 2. All the tracerends are according to the present invention bodies of revolutioni. 6.,any section at right angles with the axis is exactly circularand eachone is for the purpose of the invention marked with the respectivevalues of R and D.

The tools of an engraving-machine, as indicated in Fig. 4, are not roundin cross-section, as are the tracer ends, for they must have faces 1 toproduce edges 2 that will cut as they rotate. Hence the elements of thetracer end, Fig. 3, are not reproduced along the faces 1 of the tool,but along the cutting edges 2 of it. So in making a tool which shall be,tor instance, a tenth of the tracer end having the elements R and D, asindicated in Figs. 3 and 4, the respective adjusting devices of thegrinding-machine are not set to one-tenth R andone-tenth D,respectively, but to such values as will'give the elements one-tenth Rand one-tenth D to-the tool edges. Now when a tool withalternate flatsand edges is at work the sides of-the hole or of the gutter which itcuts have a radius less than that ofthe faces. So either graphically ormathematically the corresponding radii of faces and edges are determinedfor each type of tracer end.

I must point out that the tracers and tools of this invention can neverbe conical in form-that is to say, their sides can-never be 1 straightlines-because of the influence of the constant element R.

I claim A tracer and tool for use in a pantograph engravingrnachine,each formed of a rod having a curved working end lying in a surface ofrevolution about the aXis of its rod, the contours of said end beingdefined by two finite-geometrical distances, viz., the radius ofcurvature of saidcurved end and the perpendicular distance of the centerof this curvature from the axis of the rod; the said distances being soshort as to produce a perceptible curvature; the said distances for thetraper being proportional to those for the too In witness whereof I havehereunto set my hand in'the presence of two witnesses.

MARK BARR.

Witnesses:

BERNE NADALL, CHAs. S. WoonRorFE.

